General
The support plates for the tubes of bundles mounted in indirect heat exchangers of nuclear powered generators are one of the myriad components requiring inspection after a period of service. If these support plates are permitted to deteriorate, lengths of the tubes they are designed to support will be vulnerable to the destructive forces of fluids passed through and over the tubes. Although creative energies are being applied to develop improved support structures, the simple drilled, or broached, plate has been used predominantly. These plates, in the order of 3/4" thick, have holes formed in them for the tubes and holes through which the fluids being heated are flowed.
In service, corrosion products build up on the crevice formed between the external surface of the tubes and their holes in their support plates. Analysis of this phenomena is found throughout the prior art. It is presently sufficient to point out that these accumulations have been effective in distorting the tubes, themselves, and simultaneously applying destructive force on that portion of the support plate between the tube holes and adjacent flow holes. Periodic inspection must be made to determine the extent to which cracks have been formed in these ligaments between the tube holes and flow holes. It is in this arena that the present invention functions to improve the quality in the nondestructive radiographic interrogation of these ligaments.
Parenthetically, it is to be pointed out that more recent structural forms have been evolved as alternates to support plates. Specifically, the so-called eggcrate support structure represents the attempt to eliminate the crevice in which the corrosion products threaten the integrity of the supported tubes. Portions of these support bodies must be interrogated in the same manner as the ligaments of the plates. The problem is not confined to the specific form which will subsequently be disclosed.